1. Motors Lesson 9

2. Thinking About Motors  What is a motor? Device that converts energy into mechanical motion Device that converts energy into mechanical motion  What are motors used for? Hard drives, disk drives, fans, DVD players etc.. Hard drives, disk drives, fans, DVD players etc..  How do motors work?

3. Magnets- Necessary Component of Motors  History Named for a region in Asia Minor called Magnesia Named for a region in Asia Minor called Magnesia Magnesia was the first location magnetic rocks were found Magnesia was the first location magnetic rocks were found  Earliest Uses- 11 th Century China Compass needles Compass needles Needle is made of a magnet that points towards the north pole Needle is made of a magnet that points towards the north pole

4. How Magnets Work  Magnets Attract Metals: iron, nickel cobalt Metals: iron, nickel cobalt  Why? Alignment of atomic structure of material Alignment of atomic structure of material

5. Magnetic Poles  Magnets have two poles North pole- attracts south pole, repels north North pole- attracts south pole, repels north South pole- attracts north pole, repels south South pole- attracts north pole, repels south  Easy way to determine north vs. south pole Hold a compass next to a magnet Hold a compass next to a magnet The compass needle will point to the south pole The compass needle will point to the south pole

6. Mechanical Motion from Electricity  Hans Christian Oersted Discovered relationship in 1800’s between: Discovered relationship in 1800’s between: Mechanical ForceMechanical Force MagnetismMagnetism ElectricityElectricity Followed up by Maxwell, Farady and Lorentz Followed up by Maxwell, Farady and Lorentz

7. Mechanical Motion from Electricity  Basis for Electric Motor A wire conducting current will experience a force when it is placed in a magnetic field A wire conducting current will experience a force when it is placed in a magnetic field F = iL x B F (Force) F (Force) i (Current) i (Current) L (Length of Conductor) L (Length of Conductor) x (Cross Product) x (Cross Product) B (Magnetic Field Strength) B (Magnetic Field Strength)

8. Mechanical Motion from Electricity  Vectors Vectors represent a quantity with a size and direction Vectors represent a quantity with a size and direction  According to the formula: The force is a cross product of the vectors B and iL The force is a cross product of the vectors B and iL Cross Product: takes two vectors B and iL and produces a third: BiLsin(Ө) Cross Product: takes two vectors B and iL and produces a third: BiLsin(Ө) We will only consider vectors at right angles: F= iLB We will only consider vectors at right angles: F= iLB

9. Mechanical Motion from Electricity Right Hand Rule Used to find the direction of the force on the wire Used to find the direction of the force on the wire Point hand with open palm in direction of first vector in the cross product (iL) Point hand with open palm in direction of first vector in the cross product (iL) Close fingers in the direction of second vector (B) Close fingers in the direction of second vector (B) Your thumb is now pointing in direction of F Your thumb is now pointing in direction of F

10. Practice the Right Hand Rule!!!

11. Inside a Motor  Force on current (i) in a magnetic field can be turned into torque Simple: run current through a loop of wire in a magnetic field Simple: run current through a loop of wire in a magnetic field Current switches direction based on what side of the loop it is on Current switches direction based on what side of the loop it is on Results in a pair of forces which cause torque Results in a pair of forces which cause torque The loop will align with the magnets but will not spin The loop will align with the magnets but will not spin

12. How Does a Motor Spin?  Add physical components to make current change direction Brushes: attached to power source, do not move Brushes: attached to power source, do not move Commutator: attached to the coil, spins with coil Commutator: attached to the coil, spins with coil  When commutator spins, brushes change direction which results in current switching direction  The torque will increase with more coils

13. A Motor in Pieces